1. Field of the Invention
This invention relates to a module of a non-radiative dielectric waveguide, for example a non-radiative dielectric waveguide module used in a millimeter wave integrated circuit a millimeter wave transceiver, automotive radar system and the like.
2. Description of the Prior Art
The non-radiative dielectric waveguide (NRD guide) has a structure in which dielectric strips are provided between a pair of parallel flat conductors disposed in a space of 1/2 or below of a used high frequency signal wavelength .lambda.. With an NRD having such a structure, high frequency signals having a wavelength larger than .lambda. are cut off and cannot enter into the space between the parallel flat conductors. Furthermore, high frequency signals can be transmitted along the strip, and radiations from the dielectric wave guide are suppressed by the cut-off effects of the parallel flat conductors.
It is known that modes of propagation on NRD guide are an LSM mode and an LSE mode. Generally, the LSM mode is used because of its small loss.
Furthermore, since in such an NRD guide, by providing a dielectric strip in a curved shape, a high frequency signal can propagate easily along it, small circuit size or any other convenient circuit design can be easily implemented.
As a material for the dielectric strip, resins such as Teflon and polystyrene have been used in view of its easy processability.
However, in an NRD guide provided with a dielectric strip formed from such a resin, there is a transmission loss at a curved portion (to be simply called bending loss) or a transmission loss in a line conjugating portion is large, and for example, there is a problem that an abrupt bend having a small radius of curvature cannot be formed. Furthermore, when a gentle bend having a large radius of curvature is formed, the radius of curvature should be established precisely. Furthermore, the band width of a bend is extremely narrow as about 1 to 2 GHz in the vicinity of 60 GHz. In an NRD guide equipped with dielectric strips formed from such a resin, the dispersion curves of LSM mode and LSE mode are close to each other as shown in FIG. 22 below. As a result, the frequency difference between these modes is a very small value of about 3 GHz. Thus, a part of electromagnetic waves of the LSM mode is converted to LSE mode.
There is also an NRD guide using alumina as a material of the dielectric strip. However, in this case, to be used in a high frequency region of at least 50 GHz, the width of a strip should be markedly narrow. It is extremely difficult to process or mount the strip and this NRD guide is not practical.